Question 124866
You have q quarters and d dimes.  Since you have 12 coins, all of which are either quarters or dimes, {{{red(q+d=12)}}}: Equation 1 of your system.


Also, the value of a quarter is 25 cents, so the value of all your q quarters is 25q cents.  Likewise the value of your d dimes is 10d cents.


The total value of your money is $1.95, which can be expressed as 195 cents, therefore:

{{{red(25q + 10d=195)}}}:  Equation 2 of your system.  Alternatively, if you didn't want to convert the $1.95 to cents, you could express the value of the quarters as .25q and the value of dimes as .10d, making the equation {{{0.25q+0.10d=1.95}}}.  I would rather deal with integer coefficients myself, but it is purely a matter of personal preference.  Given proper solution methods and correct arithmetic, you will get the same answer either way.


So, how many of each coin do you have?